1. Field of the Invention
The present invention relates to a process for the production of iron oxide fine powder of high purity suitable for use in manufacturing ferrite magnets and other applications. More particularly, it concerns a process for producing high purity iron oxide fine powder from a naturally occurring oxide iron ore such as hematite (comprised predominantly of Fe.sub.2 O.sub.3), magnetite (comprised predominantly of Fe.sub.3 O.sub.4), or a mixture thereof by physical refining of the ore.
2. Prior Art
Fine powder of ferric oxide (Fe.sub.2 O.sub.3) useful for the manufacture of ferrite magnets is most commonly produced from a waste pickling solution generated voluminously in steelworks. From the waste solution which contains iron as a chloride or sulfate salt depending on the acid used in the pickling treatment, the iron value contained therein is recovered ahd then roasted to yield iron oxide. See, for example, Japanese patent Laid-Open application Nos. 58-151335 and 48-73414.
However, the use of ferrite magnets has been increasing, resulting in an increased demand for high purity iron oxide fine powder as a raw material therefor. In order to meet the increased demand, iron ores have also been used to produce iron oxide fine powder. According to one process heretofore developed in the art to produce iron oxide fine powder from iron ore, a sulfide iron ore such as pyrite or pyrrhotite is finely ground and then classified to remove coarse particles. The classified powder is then concentrated by flotation using a xanthate as a collector and finally roasted to give iron oxide fine powder. Another process starting from magnetite (Fe.sub.3 O.sub.4) involves finely grinding the magnetite ore to a particle size in the range of from 0.1 to 5 .mu.m followed by magnetic separation and refining.
A similar process starting from hematite which is first finely ground and then subjected to magnetic separation is disclosed in Japanese patent Laid-Open application No. 58-20730.
The iron oxide as a raw material for a ferrite has to possess the quality specified in JIS-K-1462 in order to achieve the desired magnetic properties in the ferrite product. Specifically, it is required to have a content of various impurities such as SiO.sub.2, Al.sub.2 O.sub.3, sulfates and chlorides which do not exceed the prescribed upper limits as shown in Table 1 below which is the same as Table 1 annexed to JIS-K-1462.
TABLE 1 ______________________________________ Specifications for iron oxide for manufacture of ferrites as defined in JIS-K-1462 Class 1 Class 2 Class 3 ______________________________________ % Fe.sub.2 O.sub.3 .gtoreq.99.0 .gtoreq.98.8 .gtoreq.98.5 % Loss on drying .ltoreq.0.30 .ltoreq.0.30 .ltoreq.0.30 % SiO.sub.2 .ltoreq.0.01 .ltoreq.0.06 .ltoreq.0.30 % Al .ltoreq.0.02 .ltoreq.0.02 .ltoreq.0.05 % Mn .ltoreq.0.30 .ltoreq.0.30 .ltoreq.0.30 % Ca .ltoreq.0.01 .ltoreq.0.02 .ltoreq.0.04 % SO.sub.4.sup.2- -- .ltoreq.0.20 .ltoreq.0.30 % Cl.sup.- -- .ltoreq.0.15 .ltoreq.0.15 ______________________________________
In the above table, the specifications under Class 1 are for iron oxide powder for use in the manufacture of soft ferrites which are widely employed as magnetic cores. Class 3 is for iron oxide powder for use in the manufacture of hard ferrites which are useful as permanent magnets. The iron oxide powder specified under Class 2 is useful for the manufacture of both hard and soft ferrites.
Using the prior art processes mentioned above, however, it is difficult to produce powdery iron oxide products of high purity which meet the requirements shown in the above specifications. For example, the iron oxide product from a waste pickling solution inevitably contains, an appreciable amount of sulfates or chlorides which come from the acid. It is difficult to remove these impurities from the product substantially completely and in addition the production cost is relatively high because the process includes a costly roasting step. Similarly, in the process starting from a sulfide iron ore, it is difficult to lower the sulfate content of the iron oxide product to the desired level and, in addition, a costly roasting step is included. The process starting from magnetite involves the step of finely grinding the ore prior to magnetic concentration, thereby frequently decreasing the refining efficiency in the magnetic concentration because fine particles of impurities tend to be entrained by iron oxide particles being collected magnetically. The latter two processes starting from iron ores are also disadvantageous in that the starting materials are restricted to particular, less commonly employed iron ores such as magnetite and sulfide iron ores (pyrite, pyrrhotite).
Accordingly, there is still a need for a suitable process of producing high purity iron oxide fine powder inexpensively from an iron ore to satisfy the increasing demand for such powder.
Thus it is an object of the present invention to provide a process for the production of high purity iron oxide fine powder from an oxide iron ore by means of only physical treatment and without chemical reaction such as roasting.
Another object of the invention is to provide a process for the production of high purity iron oxide fine powder which meets the requirements for purity as specified in JIS-K-1462 under Class 3.
A still further object of the invention is to provide a process for the production of high purity iron oxide fine powder from an oxide iron ore of the types which are commonly employed in steelworks and which are readily available.
These and other objects as well as the scope, nature and utilization of the present invention will be apparent to those skilled in the art from the following description and appended claims.